Electrolytic decomposition with permselective diaphragms



s. G. OSBORNE ET AL 2,967,806

ELECTROLYTIC DECOMPOSITION WITH PERMSELECTIVE DIAPHRAGMS Filed April 2, 1953 Jan 10, 1961 4 Sheets-Sheet 2 S/D/VEY G. OSBORNE GEORGE 7: M/LLE/Q INVENTORS BY AGE/VT are 2 1961 s. G. OSBORNE ET AL 2,967,806

ELECTROLYTIC DECOMPOSITION WITH PERMSELECTIVE DIAPHRAGMS Filed April 2, 1953 4 Sheets-Sheet 3 Wafer //7/ef fled/Tons Ouf A node 1 Jan. 10, 1961 s. G. OSBORNE ETAL 2,967,306

ELECTROLYTIC DECOMPOSITION WITH PERM-SELECTIVE DIAPHRAGMS Filed April 2, 1953 4 Sheets-Sheet 4 BY a? yure 4 AGE/VT ELECTROLYTIC DECOMPOSITION WITH PERM'SELECTIVE DIAPHRAGMS Sidney G. Osborne, SaintDavids, Ontario, Canada,,and George T. Miller, Lewiston, N .Y., assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed Apr. 2, 1953, Ser. No. 346,365

4 Claims. (Cl. 204-.72)

2,967,806 Patented Jan. 10, 1961 I impermeability to ions of the opposite charge, under the influence of an electrical current and when wet with electrolyte. Permselective diaphragms which selectively permit the passage of anions are designated as anionic; those I 4 5 which selectively permit the passage of cations are designated as cationic.

In our copending application S.N. 306,362 we have described and claimed various novel methods for eifecting.

the electrolysis of salts of organic aliphatic acids which comprise: introducing the salt to be electrolyzed into a multicompartment electrolytic cell having anode and cathode containing compartments, the anode being in contact with a liquid electrolyte containing the organic aliphatic acid resulting from the electrolysis of said salt,

This invention relates to the electrolytic decompositionthe c e being in Contact with a liquid electrolyte of substances which gives rise to electrode products normally subject to decomposition at the electrodes, to the recovery of such electrode products, and to apparatus therefor. In particular, this invention relates to the eleccontaining the cation resulting from the electrolysis ofsaid salt; interposing a permselective diaphragm between the anode and cathode; maintaining the diaphragm wet with electrolyte; impressing a voltage across said electrolysis of salts of organic aliphatic acids whereby detrodes; and recovering the products of electrolysis so procomposition of the acid at the anode is substantially acids, and derivatives thereof, which, upon electrolysis,-

are oxidized at the anode or otherwise decomposed in the; electrolytic cell, resulting in low recovery of the products.

This application is a continuation-in-part of our copending application S.N. 306,362, filed August 26,1952, now abandoned.

an anionic permselective diaphragm, whereby the acid is produced in a compartment adjacent to the anode com- Heretofore, in the electrolysis of organic aliphatic acid salts, for example, even when employing a porous diaphragm, the negative radical or ion which may be designated RCOO- migrates to the anode and, inthe absence of any material with which it can readily unite, decomposes to form carbon dioxide and a hydrocarbon. This? is in accordance with the well known Kolbe synthesis].

Under special conditions, as inlthe HoefereMoest reaction, an alcohol may be produced at the anode. However, it has been generally accepted that the electrolysis of duced from their respective electrode compartments. In these methods the acid is produced in the anode compartment. In the present invention we have found methods whereby the salt to be electrolyzed is introduced into 25 the third compartment of a multicompartment cell having a first compartment containing an anode, and a second compartment adjacent to the anode compartment which is separated from it by a cationic permselective diaphragm, andwhich is separated from the third compartment by partment. In these methods the permselective diaphragms wet with electrolytes are manipulated in such manners as to produce a product containing the organic aliphatic acid in a compartment adjacent to the anode compartment.

By these methods advantages may be obtained which could not be accomplished when the acid was produced in the anodecompartment: higher etficiencies and yields may be attained than would be obtained if the acid were 40 produced in the anode compartment, the acid may be does not result in the formation of the, acid .in quantity suitable for separation on an economic scale. Therefore,

withdrawn at higher solution concentrations without the "problem of decomposition which might arise if the same.

concentration of organic aliphatic acid were used in a cell producing the acid in the anode compartment, the

electrochemical methods have not been available for the 5 permselective diaPhragmS could be alTaIlged ill the cell simple conversion of salts of such organic aliphatic acids to the free acids and the corresponding base;v it has been necessary in order to effect these conversions to resort 1 to the chemical process of treating. such salts with a. mineral acid, thereby liberating the free acidv but at the,.5

' acids may be electrolyzed by the method which comprises:

expense of converting the base to a less valuable inorganic salt, such as the sulphate or chloride.

It is, therefore, a particular object of.this invention to provide an electrolytic process for the commercial de-x composition of salts of organic aliphatic acids whereby the corresponding free acid and free base maybe separately recovered. Another object of this invention is to effect the electrolysis so that the acid and alkali produced are not of necessity contaminated with its salt.- It is also;

an object of this invention to provide an v electrolyticcell for accomplishing this purpose. Other objects will become; apparent to those skilled in the art; on consideration of j the disclosures made herein.

\These and related Objects are-accomplished by the" present invention which comprises effecting the electi'ol- 765 of permselective dia 1 are characterized their so that 'many other primary and secondary products of the cell could be produced than when the acid was produced in the anode compartment; these and many other advantages will become more apparent hereinafter.

We have now found that salts of organic aliphatic introducing the salt to be electrolyzed into the cathode containing compartment of a three compartment electrolytic cell having an anode and a cathode in contact with liquid electrolytes, the center compartment of said cell being separated from the anode compartment by a cationic permselective diaphragm, and from the cathode compart' ment by an anionic permselective diaphragm; maintaining said diaphragms wet with liquid electrolyte; impressing a voltage across said electrodes; and recovering the acid and cation so produced from the center andcathode comthird compartment by an anionic permselective diaphragm, e

" and the thirdcompartment from the cathode compartment by a cationic permselective diaphragm; maintaining said diaphragms wet with liquid electrolyte; impressing a voltage across said electrodes; and recovering the acid and cation so produced from the second and cathode compartments repsectively.

We have also found that by adding to the anolyte a soluble ionized compound which gives rise to hydrogen ions during electrolysis, different products of the cell and other advantages may be obtained therefrom. Soluble compounds such as sodium sulfate will give rise to hydrogen ions upon electrolysis. Other soluble ionized inorganic acids such as sulfuric acid and hydrochloric acid will give rise to hydrogen ions immediately upon solution in the anolyte as well as during electrolysis. The presence of these hydrogen and/ or other ions tends to increase the over-all conductivity of the anolyte, which in turn enables higher current densities to be used at lower voltages. In addition, in those methods of electrolysis wherein the organic aliphatic acid is formed in the anode compartment, the increased hydrogen ions resulting from the addition of the soluble ionized compound aforementioned will depress the ionization of the organic aliphatic acid. This results in even less decomposition of the organic aliphatic acid at the anode. Further, if the soluble ionized compound which gives rise to hydrogen ions during electrolysis is composed of an anion which has a greater tendency to discharge at the anode than hydroxyl ion, it will discharge in preference to the hydroxyl ion and thereby may form a different primary product of the cell rather than oxygen which is produced when the hydroxyl ion is discharged. For instance, if a soluble chloride such as hydrogen chloride is used, a primary product of the cell will be chlorine gas. Also if the organic ali phatic acid is formed in the anode compartment; the" product derived fromthis compartment will be amix ture" of the soluble ionized compound and the organic aliphatic acid. Further in the processes of the present invention where the organic aliphatic acid is produced in the compartment adjacent to the anode compartment, the organic aliphatic acid will not be mixed with the soluble compound but its solution will contain the cations resulting from the electrolysis of the anolyte. If soluble ionized compounds such as hydrogen chloride or sulfuric acid are used, these cations will be hydrogen ions which will unite with the organic aliphatic acid radicals to produce the organic aliphatic acid. Similarly if a soluble ionized compound is used which is composed of cations other than hydrogen ions, such-as sodium sulfate, these cations. will" be found in the compartment adjacent to the anode compartment and the product from this compartment in the processes of the present invention may contain a mixture of organic aliphatic acid and the sodium salt of" the organic aliphatic acid.

Further we have found novel methods for advantageously employing the loss in current efiiciency inherent in the use of permselective diaphragms in these electrolytic cells, caused by undesirable leakage, migration or adsorption of a useful product into or through the diaphragm under the influence of a concentration gradient. These diaphragms are known to be less permselective at high solution concentrations and are much more nearly 100 percent permselective at lower solution concentrations. 7

If the cationic diaphragm, which should prevent the hydroxyl ions from migrating through it, is not 100 percent permselective, the hydroxyl ions will leak through the.

diaphragm into the next adjacentcompartment causing a reduction in current efiiciency. This loss in elficieucy.

may be reduced by maintaining lower solution concentra-v trons than those which may be economically desirable;

We have found various methods for. advantageously cir-- cumventing these traits inherent in the present permselec+ tive diaphragms.

Among the methods we have found for overcoming the aforesaid disadvantages is by the use of two cationic permselective diaphragms to separate the cathode compartment from the compartment which was previously adjacent to it, to form a compartment between them, into which water is introduced whereby the concentration of the base in contact with the cationic permselective diaphragm second from the cathode, is very dilute in comparison to the concentration of the base in the cathode compartment incontact with the cationic permselective diaphragm first from the cathode. In this manner the cationic permselective diaphragm second from the cathode is greatly increased in its permselectivity, and the base thereby substantially prevented from passing into the next adjacent compartment. The weak base so produced in the compartment between the two cationic diaphragms, is transferred back into the cathode compartment by way of a conduit in communication between the two compartments. Another technique for reducing the loss of efficiency resulting from the imperfect permselectivity of the permselective diaphragms, involves forming an additional compartment next to the cathode compartment, as above, by using an asbestos diaphragm facing the cathode and the cationic permselective diaphragm second from the cathode, as above, introducing water between said diaphragms and allowing the solution to slowly percolate through the asbestos diaphragm from the additional compar'tment into the cathode compartment. These methods are disclosed and claimed in our copending application S.Nl 267,846; filed on January 23, 1952.

Still' another technique for offsetting the efficiency is bas'edon our finding that the diffusion coeflicie'nt for sodium carbonate through a permselective diaphragm is of-the' orderofabout onetenth of theditfusion coefficient for sodium'hydroxide-through such diaphragms under the same conditions, andinvolves' passing carbon dioxide into the catholyte either in the cathode compartment of the cell} or" outside tlie cell, to cause the formation and separation of the c'arbonate rather than the hydroxide as a product of the cell. Still' further, we have now found that the advantages of employing permselective diaphragms inelectrolytic cells for the electrolytic decomposition of salts of organic aliphatic acids may be realized, without the concomitant undesirable effects resulting from the-adsorption, anddiffusion of liquid or soluble products ofelectrolysis fromthe cathode compartment toward the anode compartment, and with the production of a separately'recoverable' added product of the cell. These advantages may be'realized' by employing a permselective diaphragm structure in the electrolysis of salts of organic aliphatic acids in electrolytic cells, said structure comprising two cationic permselective diaphragms separated from each other to form an additional compartment, containing' an inlet for introducing a chemical reactive with the products of electrolysis migrating from the cathode compartment into theadditional compartment, and containing an outlet for removing the products so produced. When the reactive chemical addedto the diaphragm structure is:carbon dioxide the added product of the cell will be the carbonate and under controlled conditions may be thc-bicarbonateof the cation of the salt of the organic aliphatic acid. We have also. found that we can elfectively regulate the ratio of this'separately recoverable prodnet to hydroxide produced when employing this diaphra'gm" type structure by'controlling the concentration of the hydroxideproduct' in the cathode compartment andZor-the concentration of the separately recoverable product inthe-center compartment of the diaphragm structure. Chemicals other than carbon'dioxide may be used in thesediaphragmstructures which react with the hydroxylions migrating'into the structure. Sulfur di' oxide',.hydrogen.sulfide, hydrogen chloride, phosphoric acid .oreven organic acids may. be used when it is desired to produce their. resulting products from the cell and-to This diaphragm type structure may be used in any of the processes of this invention as depicted in Figures 2' and 3 and is specifically depicted in Figure 4 wherein the process of Figure 2 is described to include this structure. In addition the structure may be used in the processes described in our copending application S.N. 306,362, filed August 26, 1952. This structure may consist of two diaphragms, one a cationic permselective diaphragm and the other an asbestos diaphragm, or the two diaphragms may be both cationic permselective or both asbestos, the choice of which will depend on the particular organic aliphatic acid salt to be electrolyzed, the particular process to be employed, and the solution concentrations to be desired in the cell compartments.

In order that this invention may be more readily un derstood, it will be described with reference to the electrolysis of sodium acetate to produce acetic acid at the anode compartment or in an adjacent compartment and sodium hydroxide at the cathode as primary products of the cell, and with reference to the appended drawings. In addition, our invention is explained in accordance with the best understanding of the theories and mechanisms involved which we believe to be correct at this time. However, it is to be understood that this invention is not limited to the electrolysis of sodium acetate, or, the appended drawings, or, the explanation of the theoretical mechanisms given, as will be evident from the disclosure made herein.

The Figures 1 through 4 are diagrammatic drawings of electrolytic cells for effecting the processes of this invention and are illustrated for the electrolysis of'sodium acetate to produce acetic acid and sodium hydroxide as' primary products of the cell. Many modifications other than depicted in the drawings are contemplated as will become evident hereinafter.

Referring to Figure l:

The electrolytic cell comprises a vessel 1 separated into an anode compartment 2, and a center compartment 3 and a cathode compartment 4, by a permselective cationic diaphragm 5 and a permselective anionic diaphragm 6. The anode compartment contains an anode 7 in contact with the anolyte 8, and the cathode compartrnent contains a cathode 9, in contact with the catholyte 10. The electrolytic cell is provided with outlet 14, for removal of material from the anode compartment, outlets 13 and 15 for removal of material from the cathode compartment, outlet 12 for removal of material from the center compartment and inlets 16 and 17 for introducing water into the cell. Suitable inlets for introducing other materials into the cell, means for making electrical contact to the electrodes, and in addition, any other necessary accessories for the given electrolysis are also provided. It should be particularly noted that the electrolytic cell is provided with an inlet 11 for introducing the salt of the organic aliphatic acid into the cathode compartment to be electrolyzed.

In accordance with this process sodium acetate is electrolyzed to acetic acid and sodium hydroxide in a three compartment electrolytic cell having a cationic diaphragm 5 at the anode and an anionic diaphragm 6 at the cathode, thereby forming separated anode, center and cathode compartments. Water is fed to the anode compartment 2 and the center compartment 3 and sodium acetate solution is fed to the cathode compartment 4. During such electrolysis in the electrolytic cell described, the acetate ions, derived from sodium acetate in the cathode compartment, migrate toward the anode and penetrate the anionic diaphragm because of its selective character which permits the passage of such ions toward the anode, but upon reaching the cationic diaphragm 5, are kept from passage through the cationic diaphragm because of its selective character which resists the passage of such ions; it is our theory that such acetateions form a layer at or near the face of the diaphragm opposite the anode. The hydrogen ions liberated in the anode compartment, as a result of the discharge of hydroxyl ions at the anode which are derived from the water contained in the anode compartment, migrate toward the cathode and penetrate the cationic diaphragm 5 into the center compartment 3 because of its selective character which permits the passage of such ions toward the cathode, but upon reaching the anionic diaphragm 6 are kept from passage through the anionic diaphragmbecause of its selective character which resists the passage of such ions; it is our theory that such hydrogen ions form a layer at or near the face of the diaphragm opposite the cathode. Therefore the acetate ions which penetrate the anionic diaphragm enter the center compartment and-combine with the hydrogen ions thereby forming acetic acid, which is removed from the cell through outlet 12. At the anode, oxygen, which is de-- rived from the water contained in the anode compartment is liberated and removed from the cell through outlet 14. The hydroxyl ions liberated in the cathode compartment as a result of the discharge of hydrogen ions at the cathode, which are derived from the water contained in the cathode compartment, associate withv the sodium ions'derived-from the sodium acetate solution also contained in the cathode compartment, and form sodium hydroxide. The combined product of sodium hydroxide and spent sodium acetate is removed from the cell through outlet 13. At the cathode, hydrogen, which is derived from the water contained in the cathode compartment, is liberated and removed fromthe cell through outlet 15. Referring to Figure 2:

The electrolytic cell comprises a vessel 1, separatedinto four compartments: a'first or anode compartment 2, a second compartment 3, a third compartment-24 anda fourth or cathode compartment 4. The first or anode compartment is separated from the second compartment by a permselective cationic diaphragm 5, the second fromthe third compartment by a permselective anionic diaphragm 25 and the third from the fourth or cathode compartment by a permselective cationic diaphragm 26. The anode compartment contains an anode 7, in contact with anolyte 8, and the cathode compartment contains I a cathode 9 in contact with catholyte 10. The electrolytic cell is provided with an outlet 14 for removal of material from the anode compartment, outlet 12 for removal of material from the'second compartment, out lets 13 and 15 for removal of material from the cathode.

compartment and inlets 16, 17 and-19 for introducing water into the cell. Suitable inlets for introducing other materials into the cell, means for making electrical contact to the electrodes, and in addition, any other neces sary accessories for the given electrolysis arealso provided. It should be particularly noted that the electrolytic cell is provided with an inlet 27 for introducing the salt of an organic aliphatic acid into the third compart ment to be electrolyzed. Y

In accordance with this process sodium acetate is electrolyzed to acetic acid and sodium hydroxide in a four compartment electrolytic cell having a cationic diaphragm 5 between the first or anode compartment andthe second compartment, and anionic diaphragm 25 be-{ I tween the second and third compartments, anda ca: tionic diaphragm 26 between the third and the fourth or the cathode compartments. Water is fed into the first or anode compartment 2, the second compartment 3 and the fourth or cathode compartment 4 and sodium acetate solution is fed into the third compartment "24.

During such electrolysis in the electrolytic-cell describedf passage of such ions toward the anode, but uponfreacli ing the cationic diaphragm'fS are kept from passage;

through the cationic diaphragm because of itsselecti e1 character which resists the passage of such ions; audit is our theory that such acetate ions form a layer at or near the face of the diaphragm opposite the anode. The hydrogen ions liberated in the anode compartment 2, as a result of the discharge of hydroxyl ions at the anode which are derived from the water contained in the anode compartment, migrate toward the cathode and penetrate the cationic diaphragm into the second compartment 3 because of its selective character which permits the passage of such ions toward the cathode, but upon reach ing the anionic diaphragm 25 are kept from passage through the anionic diaphragm because of its selective character which resists the passage of such ions; it is our theory that such hydrogen ions form a layer at or near the face of the diaphragm 25 oppositethe cathode. Therefore the acetate ions which penetrate the anionic diaphragm 25 enter the second compartment 3 and combine with the hydrogenionsthereby forming acetic acid, which is removed from the cell through outlet 12. At the anode, oxygen, which is derived from the water contained in the anode compartment, is liberated and removed from the cell through outlet 14. During electrolysis, the sodium ions, derived from the sodium acetate solution contained in the third compartment 24, migrate toward the cathode and penetrate the cationic diaphragm.

26 because of its selective character which permits the passage of such ions toward the cathode. The hydroxyl ions liberated in the cathode compartment 4, as a result of the discharge of hydrogen ions at the cathode which are derived from the water contained in the cathode compartment, are attracted toward the anode, but, are kept from passage through'the cationic diaphragm 26 because of its selective character which resists passage of such ions; itisourtheory that such hydroxyl ions form a layer at or near the face of the diaphragm 26 opposite the cathode. The sodium ions which penetrate the cationic diaphragm 26 enter into the cathode compartment and associate with the hydroxyl ions thereby forming sodium hydroxide which is removed from the cell through outlet 13. At the cathode, hydrogen, which is derived from the water contained in the cathode compartment, is liberated and removed from the cell through outlet 15.

Referring to Figure 3:

The electrolytic cell comprises a vessel 1, separated into anode compartment 2, a center compartment 3, and a cathode compartment 4, by a permselective anionic diaphragm 21 and a permselective cationic diaphragm 18. The anode compartment contains an anode 7, in contact with anolyte 8, and the cathode compartment contains a cathode 9, in contact with the catholyte 10. The electrolytic-cell is provided with outlets 22 and 14 for removal of material from the anode compartment, outlets 13 and 15 for removal of material from the cathode compartment and inlet 19 for introducing water into the cell.

Suitable inlets for introducing other materials into the cell, means for electrical contactto the electrodes, and in addition, any other necessary accessories for the given electrolysis are also provided. It should be particularly noted that the electrolytic cell is provided with an inlet 20 for introducing the salt of an organic aliphatic acid into the center compartment to be electrolyzed, and an inlet 23 for introducing a soluble ionized compound which gives rise to hydrogen ionseither before and/0r during'electrolysis into the anode compartment to be electrolyzed.

In accordance with this invention sodium acetate is electrolyzed to acetic acid and sodium hydroxide in a three; compartment electrolytic cell having an anionic diaphragm 21 at the anode, and, a cationic diaphragm 18, at the cathode, thereby forming separated anode, center'and cathode compartments. Sulfuric acid solution is fed to the anode compartment 2, sodium acetate solution is fed'to the centerco'm'partment 3 and water is fed to the cathode compartment 4. During such electrolysis in the electrolytic cell described, the acetate ions, derived from sodium acetate in the center compartment 3, migrate toward the anode-and penetrate the anionic diaphragm 21 because of its selective character which permits the passage of such ions toward the anode. The hydrogen ions liberated in the anode compartment, as a result of the discharge of hydroxyl ions at the anode which are derived from the water contained in the anode compartment, are attracted toward the cathode but, are kept from passage through the anionic diaphragm 21 because of itsse lective character which resists the passage of such ions; it is our theory that such hydrogen ions form a layer at or near the face of the diaphragm 21 opposite the anode; the acetate ions which penetrate the anionic diaphragm 21 enter into the anode compartment and combine with hydrogen ions at or near the face of the diaphragm thereby forming acetic acid, which is removed from the cell with the cell with the sulfuric acid solution through outlet 22. At the anode, oxygen, which is derived from the water contained in the anode compartment, is liberated and removed from the cell through outlet 14. During electrolysis, the sodium ions, derived from the sodium acetate solution contained in the center compartment 3, migrate toward the cathode and penetrate the cationic diaphragm 18 because of its selective character which permits the passage of such ions toward the cathode. The hydroxyl ions liberated in the cathode compartment, as a result of the discharge of hydrogen ions at the cathode which are derived from the water contained in the cathode compartment, are attracted toward the anode, but, are kept from passage through the cationic diaphragm 18 because of its selective character which resists passage of such ions; it is our theory that such hydrox'ylions'forma layer at or near the face of the diaphragm 18opposit e the cathode. The sodium ions which penetrate the cationic" diaphragm 18 enter into the cathode'compartment and associate with the hydroxyl ions thereby forming sodium hydroxide, which is removed from the cell through outlet 13. Hydrogen, which is derived from th'e'water contained in the cathode compartment, is liberated at the cathode and removed from the cell through outlet 15.

Referring to Figure 4:

The electrolytic cell comprises a vessel 1, separated into five compartments. The first or anode compartment 2, the second compartment 3, the third compartment 24, the fourth compartment 28 and the fifth or cathode coinpartment 4. The first or anode compartment 2 is separated from the second compartment by a permselective cationic diaphragm 5, the second from the third compartment by a perm'selective anionic diaphragm 25, the third from the fourth compartment by a permselective cationic diaphragm 29, and the fourth from the fifth or cathode compartment by a permselective cationic diaphragm 30. The anode compartment contains an anode 7, in contact with anolyte 8, and the cathode compartment contains a cathode 9, in contact with catholyte 10. The electrolytic cell is provided with outlet 14 for removal of material from the first or anode compartment 2, outlet 12 for removal of material from the second compartment 3, outlet 31 for removal of material from the fourth compartment 28, outlets l3 and 1-5 for removal of material from the fifth or cathode compartment 4, and inlets 16, 17, 32 and 19 for introducing water into the cell. Suitable inlets for introducing other materials into the cell, means for making electrical contact to the electrodes, and in addition, any other necessary accessories for the given electrolysis are also provided. It should beparticularly noted that the electrolytic cell is provided with inlet 32 for introducing a chemical compound such as carbon dioxide into the fourth compartment 23'and inlet 27 for introducing the salt of an organic aliphatic acid into the third compartment 24 to be electrolyzed. I a

In accordance with this process sodium acetate is electrolyzed to acetic acid, sodium hydroxide and sodium carbonate in a five compartment electrolytic cell havinga 9 a cationic diaphragm between the first or anode compartment and the second compartment, an anionic diaphragm 25 between the second and third compartments, a cationic diaphragm 29 between the third and the fourth compartments and a cationic diaphragm 30 between the fourth and the fifth or cathode compartments. Water is fed into the first or anode compartment 2, the second 3, the fourth 28 and the fifth or cathode compartment 4, sodium acetate solution is fed into the third compartment 24 and carbon dioxide is fed into the fourth compartment 28 to form a solution of carbonic acid. During such electrolysis in the electrolytic cell described, the acetate ions, derived from sodium acetate in compartment 24, migrate toward the anode and penetrate the anionic diaphragm 25 into the second compartment 3 because of its selective character which permits the passage of such ions toward the anode, but upon reaching the cationic diaphragm 5 are kept from passage through the cationic diaphragm S because of its selective character which resists the passage of such ions; and it is our theory that such acetate ions form a layer at or near the face of the diaphragm 5 opposite the anode. erated in the anode compartment 2, as a result of the discharge of hydroxyl ions at the anode which are derived from the water contained in the anode compartment, migrate toward the cathode and penetrate the cationic diaphragm 5 into the second compartment 3 because of itsselective character which permits the passage of such ions toward the cathode, but upon reaching the anionic diaphragm 25 are kept from passage through the anionic diaphragm because of its selective character which resists the passage of such ions; it is our theory that such hydrogen ions form a layer at or near the face of the diaphragm 2'5 opposite the cathode. Therefore, the acetate ions which penetrate the anionic diaphragm 25 enter the second compartment 3 and combine with the hydrogen ions thereby forming acetic acid which is removed from the cell through outlet 12. At the anode, oxygen, which is derived from the water contained in the anode compartment, is liberated and removed from the cell through outlet 14. During electrolysis, the sodium ions, derived from the sodium acetate solution contained in the third compartment 24 migrate toward the cathode and penetrate the cationic diaphragm 29 into the fourth compartment 28 and the cationic diaphragm 30 into the fifth or cathode compartment 4 because of the diaphragms selective character which permit the passage of such ions toward the cathode. The hydroxyl ions liberated in the cathode compartment 4, as a result of the discharge of hydrogen ions at the cathode which are derived from the water contained in the cathode compartment, are attracted toward the anode and these hydroxyl ions tend to be kept from passage through the cationic diaphragm The hydrogen ions lib-- 30 because of its selective character which resists passage 7 to such ions; it is our theory that such hydroxyl ions form alayer at or near the face of the diaphragm opposite the cathode. The sodium ions which penetrate the cationic diaphragm 30 enter into the fifth or cathode compartment 4 associate with the hydroxyl ions thereby forming sodium hydroxide, which is removed from the cell through outlet 13. However, because of the lack of complete permselectivity of the cationic diaphragm 30 some of the hydroxyl ions and/or sodium hydroxide leak into thefourth compartment 28 and react with the carbonic acid and sodium ions to form sodium carbonate which is removed from the cell through outlet 31. At the cathode, hydrogen, which is derived from the water contained in the cathode compartment is liberated and removed from the cell through outlet 15.

This invention is further illustrated by the following examples which are not to be construed as limiting.

Example 1 A concentrated solution of sodium acetate was eleclmlyzed in an ordinary two-compartment electrolytic cell h'a'viag'a graphite anode, an asbestos diaphragm steel cathode. The cathode'compartment contained water and the anode compartment contained the aqueous concentrated sodium acetate solution to be electrolyzed. After operating the cell for approximately two hours, the current efiiciencies obtained, which were calculated from the analysis of the anolyte and catholyte, employing a copper coulometer to measure the current, were as follows: current efiiciency on acetic acid: zero percent; current efliciency on caustic soda: 26.5 percent.

Example 2 Example 1 was repeated except that a permselective cationic diaphragm was employed in the two-compartment cell in place of the asbestos diaphragm. After operating the cell for approximately two hours the current efficiency on acetic acid was found to be 12 percent, and on caustic soda: 71 percent.

Example 3 Example 4 A concentrated solution of sodium acetate was introduced into the center compartment of a three compartment cell. The anode compartment contained a graphite anode and was separated from the center compartment by an anionic diaphragm and was filled with water. The cathode compartment which was separated from the center compartment by a cationic diaphragm contained a steel cathode and was also filled with water. After operating the cell for approximately two hours the current efliciency on acetic acid was found to be 86.4 percent, and on caustic soda: 84 percent.

Example 5 Example 3 was repeated except that carbon dioxide gas was bubbled through the cathode compartment. After operating approximately two hours the current efficiency on acetic acid was found to be 87 percent and on sodiumcarbonate': percent.

These results may be summarized as follows:

Diaphragm Current Etfieiency,

percent Anode Cathode Acetic Caustic Soda Acid Ex. 1 Asbestos 0 2G. 5 Ex. 2 Cationic 12, 71 Ex. 3 Asbestos Asbestos 58. 6 47 Ex. 4 Anionic... Cationic 86. 4 84 Ex. 5 Anionic. Cationic-H302 87 95 (NazCOQ In the above examples a graphite anode was used but showed considerable disintegration. Nickel is fairly resistant, magnetite is excellent and platinum appears to give no trouble.

Example 6 Example 5 was repeated except that a solution of percent acetic acid was used as anolyte instead of water alone, and substantially no current flowed at seven'volts potential difference across the electrodes within. the first minute, was also the case when water alone was '11 used as anolyte, namely that substantially no current. flowed during the first minute Example 7 Example 8 Example 7 was repeated except that the anolyte was made one-tenth normal with sulfuric acid, and substantially 90 amperes per square foot of diaphragm flowed at six and one half volts potential difference across the electrodes within the first minute.

Examples 6, 7 and 8 show'the vast improvement in the voltage-amperage relationship which can be obtained when the anolyte contains a compound which gives rise to hydrogen ions during electrolysis, i.e. when the anolyte contains a strong electrolyte. When soluble ionized compounds such as soluble sulfates including sulfuric acid, are used, the gaseous product given off at the anode will be oxygen. However when compounds such as the soluble chlorides including hydrochloric acid are used the product given 01f at the anode will be gaseous chlorine;

Sodium formate was also electrolyzed under conditions similar to those of the foregoing examples. In addition to the above type modifications, the cell was operated using two cationic diaphragms to form a three compartment cell, the formic acid being formed in the center compartment. The-summation of'results obtained is as follows:

1 The abnormally high sodium carbonate current efliciency in Example 10 is probably due to some leakage and dircte transformation of sodium iormnte into sodium carbonate.

Sodium oxalate was also electrolyzedunder conditions similar to those of the foregoing examples. In addition two other diaphragm modified cells wereused. The cell was operated using a cationic diaphragm facing the anode and an anionic diaphragm facing the cathode to form a three compartment cell, the sodium oxalate being added to the cathode compartment and the oxalic acid beingformed in the center compartment, all similar to that depicted in Figure 1. And also the cell was divided into four compartments similar to that depicted in Figure 2 wherein the sodium oxalate was introduced into the compartment adjacent to the cathode compartment and the oxalic acid was separately recovered in the compartment adjacent to the anode compartment. The summation of results obtained is as follows:

S odium moriochldracethtewasalso electr'olyzed under conditions similar to the foregoing examples and the summation of results obtained is as follows:

Diaphragm Current Efficlency,

percent Monoehio- Caustic Anode Cathode roaeetie Soda Acid Ex. 19 Asbestos Asbestos 56 63 Ex. 20 Cationic Anionic Cationic near near 100 From a consideration of the foregoing examples, which were run as similarly as possible, so that comparisons could be made with each other, it is apparent that, as is particularly illustrated in Examples 4 and 12, successful electrolysis of solutions of salts of organic aliphatic acids can be realized whereby the acid and base are separately produced in the anode compartment and the cathode compartment respectively, and without substantial degradation of the organic component into oxidation products. It is also apparent that in accordance with the processes of the present invention as particularly illustrated by Examples 14, 17, 18 and 20, successful electrolysis of salts of organic aliphatic acids can be realized whereby the acid and cations are produced. in thecompartment adjacent to the anode compartment and the cathode compartment respectively, without substantial degradation of the organic component into oxidation products, and with higher eificiencics than when the corresponding acid is produced inthe anode compartment. This is evidenced from the data given in the tabulations under current efliciencies. The examples, particularly Examples 6, 7 and 8 and the discussion which followed Example 8 evidenced the advantages which can be derived from adding a soluble ionized compound to the anode compartment which gives rise to hydrogen ions during electrolysis. The examples also illustrated that the current efficiency on caustic soda maybe further increased as well as producing another product of the cell in accordance with this invention, and as particularly reflected in Examples 5, 13, 14, 15 and 17, by introducing into the cathode compartment a chemical such as carbon dioxide which will react with the hydroxyl ions formed at the cathode to produce sodium carbonate as a product of the cell. In like manner these examples evidence that when carbon dioxide is introduced into a cationic permselective diaphragm structure adjacent to the cathode compartment, sodium carbonate will be produced in the cationic permselective diaphragm structure and caustic soda will be produced in the cathode compartment as well. It will be noted that whether one or more'diaphragms is used, the current efficiency of its cell is invariably better when permselective diaphragrns are used according to the processes of our invention rather than porous diaphragms such as asbestos. From an over-all consideration of these examples it is apparent that high current efiiciencies may be realized by employing a permselective diaphragm in combination with a conventional diaphragm in a multicompartment electrolytic cell.

The permselective diaphragms employed in the electrolytic decompositions described in the preceding examples can be constructed using ion exchange resins which have been formed into continuous thin' sheets. When a cation active ion exchange resin is employed a cationic permselective membrane is produced, i.e., one which selectively permits passage of cations through its structure from one compartment of the cellto the next adjacent compartment in the direction toward. the attraction of its electrode under the influence of an im pressed voltage and when wet with electrolyte. When an anion active ion exchange resin is employed an anionic perselective membrane is produced, i.e., one which selectively permits passage of anions through its structure a 13 from one compartment of the cell to the next adjacent compartment in the direction toward the attraction of its electrode under the influence of an impressed voltage and when wet with electrolyte. Such membranes or sheets which are self-supporting, pliable, substantially impermeable to liquids and permselective can be made by intimately and unifornily distributing a substantial proportion of particles of an insoluble, infusible ion exchange resin into a plastic material such as those used for making plastic sheets and films for example, synthetic hydrocarbon type plastic and naturalor synthetic rubber.

The choice of permselective membranes to be employed in electrolytic cells in accordance with this invention may be varied. For example, when it is desired to produce a substantially pure cathodic product of electrolysis of a salt of an organic aliphatic acid, such as sodium hydroxide resulting from the electrolysis of sodium acetate, it is only necessary to employ a cationic permselective membrane facing the cathode and to introduce the salt to be electrolyzed into a compartment on the other side of the membrane, as illustrated in Examples 2 and 10. When it is desired to produce a substantially pure anodic product of electrolysis of a salt of an organic aliphatic acid, such as acetic acid resulting from the electrolysis of sodium acetate, it is only necessary to employ an anionic permselective membrane facing the anode and to introduce the salt to be electrolyzed into a compartment on the other side of the membrane from the anode. In addition to this a conventional membrane such as an asbestos diaphragm may be inserted in combination with the permselective membranes just described to make a multicompartment electrolyte cell. The processes of the present invention produce an organic aliphatic acid in the compartment adjacent to the anode compartment, the anode compartment being separated from the next adjacent compartment by a cationic permselective membrane and the next adjacent compartment being separated from the third compartment by an anionic permselective membrane. According to these processes, where only a pure organic aliphatic acid is desired, the salt of the organic aliphatic acid is introduced in the cathode compartment of a three compartment cell, the cathode compartment being separated from the other two compartments by an anionic permselective membrane. Also where both the pure organic aliphatic acid and the pure cationic products are desired, the salt of the organic aliphatic acid is introduced into the third compartment of a multicompartment electrolytic cell where the first or anode compartment is separated from the second adjacent compartment by a cationic permselective membrane, the second from the third by an anionic permselective membrane and the third compartment is separated from the cathode by at least one cationic permselective membrane. In addition to these methods a conventional diaphragm such as an asbestos diaphragm may be inserted in combination with or in addition to the permselective diaphragm arrangements shown to form additional multicompartment electrolytic cells for the processes of the present invention.

The attached drawings are diagrammatic sketches of electrolytic cells embraced Within the scope of this invention and are not to be confused with any actual commercial cell design. It is apparent from the basic nature of this invention that various modifications in cell design are possible. For example placement of the inlets and outlets may be made so as to favor the removal of the products of electrolysis without excessive exposure to the electrodes. The distance of the mebranes from the electrodes may be varied within wide limits; however, in order to favor compactness of the cells and low resistance, a preferred design involves placing the membranes close to the electrodes. In addition, compactness in cell design will be favored by employing a multiplicity of duplicate cells of this invention into a single unit.

The materials of construction which may beeniployed the ordinary parts of the electrolytic cells do not vary from those which have already been found applicable for any given electrolysis and are considered to be up related in so'far as limiting the scopeof this invention.

The operating conditions such as current density, applied voltage, temperature, feed and product concentrations, various additives and other conditions familiar to.v those skilled in the art are considered to be unrelated in so far as limiting thescope of this invention. a For example, when electrolyzing an aqueous salt of acetic acidv at asuitable current density such as 90 amperes per square foot, the strength'of the acetic acid being produced appears to have little effect on the current efiiciency and the anode and'cathode products are free from the ali-- phatic salt being electrolyzed. The relative qunimport'ance of maintaining critical operating conditions under this invention for effecting the electrolysis of organic-aliphatic acid salts into the acid andcation is a material advantage which allows for the practical recovery of these products. It is of course apparent that the voltage necessary in the electrolytic processes of this invention, is a voltage large enough to cause the electrolytic discharge or decomposition of the anions in the anolyte at the anode and the cations in the catholyte at the cathode, to form primary products of the cell.

Furthermore, we do not wish to be limited to the electrolysis of any particular salt or salts which have been used as examples to explain this invention, as we have found that the salts of other organic aliphatic acids can be suitably employed and are embraced within the scope of this invention. For example others which may be used are: Salts of organic aliphatic acids, such as formates, acetates, propionates, butyrates, stearates, etc.; salts of substituted aliphatic acids, such as monochloroacetates, trichloroacetates, aminoacetates, lactates, sulphoacetates, mandelates, etc.; salts of unsaturated aliphatic acids, such as acrylates, methacrylates, etc.; salts of ketonic aliphatic acids, such as acetoacetates, pyruvates, etc.; salts of polycarboxylic aliphatic acids, such as oxalates succinates, maleates, etc.; salts of cycloaliphatic acids, such as cyclopropane carboxylates; and derivatives thereof; all of which upon normal electrolysis would oxidize at or near the anode or otherwise be decomposed in accordance with the Kolbe reaction, but under this invention are successfully produced without substantial degradation of the organic component into its oxidation products. In addition, we do not intend to be limited to just the sodium salts of the organic aliphatic acids, as other soluble salts of these acids may also be used in accordance with this invention such as the potassium salts, ammonium salts, lead salts, copper salts, and other metal salts.

Various modifications may be made from the foregoing disclosure without departing from the spirit and scope of this invention and we do not intend to be limited thereto except as defined in the appended claims.

We claim:

1. A process for effecting the electrolytic decomposition of salts of organic aliphatic acids which comprises: introducing the salt to be electrolyzed into the third compartment of a multicompartment electrolytic cell, said cell having a first compartment containing an anode in contact with liquid electrolyte, a second compartment adjacent to the anode compartment containing the organic aliphatic acid resulting from the electrolysis of said salt and a cathode compartment containing a cathode in contact with liquid electrolyte, said liquid electrolyte containing the cation resulting from the electrolysis of said salt; interposing a cationic permselective diaphragm between the first compartment and the second compartment containing the organic aliphatic acid and interposing an anionic permselective diaphragm between the second compartment and the third compartment containing the salt oi the organic aliphatic aci maintaini g the diaphragms wet with electrolyte; impressing a voltage across said 'electrodes and recovering the products of electrolysis so produced.

2. A process according to claim 1 wherein the salt of the organic aliphatic acidis introduced into the cathode compartment of athree compartment electrolytic cell, the acid is withdrawn from the second compartment and the cation of the salt is withdrawn from the cathode compartment.

3. A process according to claim 1 wherein the salt of the organic aliphatic acid is introduced into the third compartment of a four compartment electrolytic cell, the

first compartment being separated from the second com-.

partment by a cationic permselective diaphragm, the second from the third by an anionic permselective diaphragm and the third compartment from the cathode compartment' by a cationic permselective diaphragm, and where the acid is withdrawn from the second compartment and the cation of the salt is withdrawn from the cathode compartment.

4. A process according to claim 1 wherein the salt of the organic aliphatic acid is introduced into the third compartment of a five compartment electrolytic cell, the

first compartment being separated from the second compartment by a cationic permselective diaphragm, the second from the third by an anionic permselective diaphragm, the third from the fourth by a cationic permselective diaphragm and the fourth compartment from the cathode compartment by a cationic permselective diaphragm, and where the acid is withdrawn from the second compartment and the cation of the salt is with drawn from both the fourth compartment and cathode compartment.

References Cited in the file of this patent UNITED STATES PATENTS 634,271 Syberg Oct. 3, 1899 2,033,732 Neiss Mar. 10, 1936 2,592,686 Groombridge et a1 Apr. 15, 1952 2,636,852 Juda et al. Apr. 28, 1953 OTHER REFERENCES Kalauch: Kolloid Zeitschrift, vol. 112 (1949), pp. 21-26.

Meyer et al.: Helvetica Chimica Acta, vol. 23 (1940), pp. 795-800. 

1. A PROCESS FOR EFFECTING THE ELECTROLYTIC DECOMPOSITION OF SALTS OF ORGANIC ALIPHATIC ACIDS WHICH COMPRISES: INTRODUCING THE SALT TO BE ELECTROLYZED INTO THE THIRD COMPARTMENT OF A MULTICOMPARTMENT ELECTROLYTIC CELL, SAID CELL HAVING A FIRST COMPARTMENT CONTAINING AN ANODE IN CONTACT WITH LIQUID ELECTROLYTE, A SECOND COMPARTMENT ADJACENT TO THE ANODE COMPARTMENT CONTAINING THE ORGANIC ALIPHATIC ACID RESULTING FROM THE ELECTROLYSIS OF SAID SALT AND A CATHODE COMPARTMENT CONTAINING A CATHODE IN CONTACT WITH LIQUID ELECTROLYTE, SAID LIQUID ELECTROLYTE CONTAINING THE CATION RESULTING FROM THE ELECTROLYSIS OF SAID SALT, INTERPOSING A CATIONIC PERMSELECTIVE DIAPHRAGM BETWEEN THE FIRST COMPARTMENT AND THE SECOND COMPARTMENT CONTAINING THE ORGANIC ALIPHATIC ACID AND INTERPOSING AN ANIONIC PERMSELECTIVE DIAPHRAGM BETWEEN THE SECOND COMPARTMENT AND THE THIRD COMPARTMENT CONTAINING THE SALT OF THE ORGANIC ALIPHATIC ACID, MAINTAINING THE DIAPHRAGMS WET WITH ELECTROLYTE, IMPRESSING A VOLTAGE ACROSS SAID ELECTRODES AND RECOVERING THE PRODUCTS OF ELECTROLYSIS SO PRODUCED. 